Do cat scratches pose a high risk of infection, or is it just cat bites?

Cat Scratches and Infection Risk

Both cat scratches and cat bites pose significant infection risks, with cat scratches specifically associated with Bartonella henselae infection (cat scratch disease) and potential for Pasteurella multocida infection, requiring prompt wound care and consideration of antibiotic treatment in high-risk cases.

Infection Risk Comparison

• Cat bites carry the highest risk of infection (30-50%) 1, 2
• Cat scratches have significant infection risk, particularly for:
  • Bartonella henselae (cat scratch disease)
  • Pasteurella multocida (especially in deep scratches)

Cat Scratch Disease

Cat scratch disease is a specific infection caused by Bartonella henselae that typically presents as:

• A papule or pustule developing 3-30 days after a scratch or bite
• Regional lymphadenopathy occurring about 3 weeks after inoculation
• Lymphadenopathy generally resolving within 1-6 months (though nodes may suppurate in ~10% of cases)
• Extranodal disease (CNS, liver, spleen, bone, lung) in ≤2% of cases 1

Treatment for Cat Scratch Disease

For confirmed cat scratch disease, the IDSA guidelines strongly recommend:

• Azithromycin as the treatment of choice:
  • Patients >45 kg: 500 mg on day 1 followed by 250 mg for 4 additional days
  • Patients <45 kg: 10 mg/kg on day 1 and 5 mg/kg for 4 more days 1

Pasteurella multocida Infection

Cat scratches, especially deep ones, can inoculate Pasteurella multocida, which:

• Causes rapidly developing cellulitis at the site of injury
• Can lead to chronic local infection of deep tissues and osteomyelitis
• Responds well to penicillin-based antibiotics 3

Management of Cat Scratches

Immediate Wound Care

1. Thorough irrigation with copious amounts of saline or water (avoid pressure irrigation as it may drive bacteria deeper)
2. Clean the wound to remove foreign material and necrotic tissue

When to Consider Antibiotics for Cat Scratches

Prophylactic antibiotics should be considered for cat scratches in the following scenarios:

• Scratches on hands, feet, face, or near joints (high-risk areas) 1
• Deep scratches that penetrate through the skin 3
• Immunocompromised patients (including HIV-infected individuals) 1
• Presence of significant inflammation or early signs of infection
• Scratches in elderly or very young patients

Antibiotic Selection

If antibiotics are indicated:

• First-line: Amoxicillin-clavulanate 500/125 mg three times daily for 5-7 days 1
• For penicillin allergy: Doxycycline 100 mg twice daily (not for children under 8) 4

Prevention Recommendations

1. Avoid activities that might result in cat scratches 1
2. Wash sites of cat scratches promptly 1
3. Do not allow cats to lick open cuts or wounds 1
4. Implement flea control for cats to reduce the risk for Bartonella infection 1
5. For immunocompromised patients, consider adopting cats older than 1 year and in good health 1

Special Considerations

• Cat scratches on the hands have the highest risk of infection and complications 5, 3
• Immunocompromised patients should be particularly cautious with cat scratches and may need lower thresholds for antibiotic treatment 1
• Most uncomplicated cat scratch disease resolves spontaneously without antibiotics 6

When to Seek Medical Attention

Seek medical care if any of the following develop after a cat scratch:

• Increasing redness, swelling, warmth, or pain
• Pus or unusual drainage
• Red streaks extending from the wound
• Fever or chills
• Swollen lymph nodes
• Symptoms persisting beyond 2 weeks